Bignoniaceous plant Tabebuia avellanedae (Taheebo) is mighty tree originally come from South America, from Brazil to north Argentina. The plant is a traditional folk medicine known from the ancient Inca period, and a bark thereof has been used as a diuretic agent or an astringent. In contrast, since the plant has been focused as a medicinal resource with anticancer, antifungus, antibacterial, antiinflammatory activities and the like, researches in extraction ingredients of the plant have been developed to isolate naphthoquinones, anthraquinones, benzofuran compounds, benzene derivatives and so on. It has been known that among these isolated ingredients 2-(1-hydroxyethyl)-5-hydroxynaphtho[2,3-b]furan-4,9-dione, referred to as NQ801 hereinafter, of the formula (III):
has a strong cytotoxicity as well as a potent cancer-preventing activity against various tumor cells (See, for example, Patent Document 1).
An extraction from the plant has been known as a method for obtaining NQ801. However, it is difficult to get the plant in large amounts, and further, it is very low yields of 0.05% by the extraction (See, for example, Nonpatent Document 1), and therefore, it is difficult to extract from the plant to get NQ801 in large amounts.
Additionally, a method for preparing NQ801 by organic synthesis is described in JP 2006-002482 (Patent Document 2), which has been found by the present inventors. The synthetic method comprises preparing NQ801 via an intermediate, 2-acetyl-5-hydroxynaphtho[2,3-b]furan-4,9-dione which is easily derived from 5-hydroxynaphthalene-1,4-dione (also known as juglone). In said method, NQ801 may be easily synthesized in a good yield by using as a starting material juglone which is commercially available as a chemical reagent at a relatively low cost. However, it is necessary to optically resolve the resulting NQ801, which is obtained in a racemic form, in a further step in order to get an optically active NQ801.    Patent Document 1: JP 2669762    Patent Document 2: JP 2006-002482    Nonpatent Document 1: Shinichi UEDA et al., Phytochemistry, 1994, Vol. 36, No. 2, p. 323-325    Nonpatent Document 2: Ryoji NOYORI et al., J. Am. Chem. Soc., 1996, Vol. 118, p. 2521-2522